This invention relates to alpha values and, more particularly, to transmission of alpha values for performing video mixing operations.
Applications for mixing digital video and personal computer (PC) graphics signals are increasingly popular. Digital video signals may be transmitted by cable, satellite, or other means, to a television display. PC graphics signals, typically generated by a software program running on a processor-based system, may be sent to a computer monitor.
A set-top box is a processor-based system that employs a television display instead of a computer monitor for viewing video signals, PC graphics signals, or a combination of the two. The set-top box may execute application software, such as electronic mail programs, connect to a data network such as the Internet using browser software, and receive and display television programming signals.
One component featured in some set-top boxes is a video mixer. The video mixer receives the digital video signal from an external source, such as via a coaxial cable connected to the set-top box, and mixes the signal with another video signal, such as a PC graphics signal, which may be generated from within the set-top box.
The video mixer may employ alpha values when combining video signals with PC graphics signals. An alpha value describes the opacity of a pixel, or picture element. The alpha value specifies how two pixels are to be combined in the video mixer. The resulting pixel may be solid, transparent, or some characteristic between the two. This combining operation is known as alpha blending.
During processing of the PC graphics and video signals, several thousand alpha values may be utilized. Because circuitry besides the video mixer may not use them, the alpha values may be routed to the video mixer only when needed. Their transmission to the mixer is thus synchronized with the video mixing operation, which typically occurs in real time.
Some prior art system transmit alpha values to the video mixer over a high-bandwidth bus such as a peripheral component interconnect (PCI) bus. For some set-top boxes, however, a lower cost alternative may be desirable.
Thus, there is a continuing need to provide a mechanism for efficiently handling alpha values during video mixing operations.